Analysis of human immunodeficiency virus type 1 promoter insertion in vivo

Our study reports the occurrence of HIV-1 insertional activation events in vivo. Using a previously described PCR assay, small aliquots of broncho-alveolar lavage (BAL) cells obtained from AIDS patients were analyzed. Nine percent (5/54) of the aliquots contained proviral-host sequence transcripts indicating HIV-1 promoter insertion, whereas multiply spliced HIV-1 mRNAs were found in 28% (15/54) of the aliquots. In four of five events, insertions affect distinct cellular transcription units expressed in a T-cell line. To establish a ratio between provirus integration and promoter insertion events, an in vitro infection study was performed and transcripts containing HIV-1 and K-ras or CD4 gene sequences, respectively, were monitored. Given the randomness of retrovirus integration, 170 sense-oriented HIV integrations into these gene loci were predicted to occur. Three distinct promoter insertion events were observed, indicating that 1.8% of integrated proviruses transcribed adjacent genes. Based on this result and a mean of 257 proviral copies per 10(6) BAL cells, we would expect to observe 25 promoter insertion events in our in vivo study. That only five events were found may be due to the lower transcriptional activity of HIV-1 in vivo than that in cell cultures.